More specifically, the invention relates to a device which can be inserted in a machine for making absorbent sanitary articles such as disposable nappies for children or adults.
As is known, these articles are obtained by laying a sheet of impermeable material over a sheet of permeable material (of non-woven fabric), with a padding consisting of an absorbent pad interposed between the two sheets. More specifically, both in the case of nappies of children and in the case of nappies for adults, it is usual to add accessory components such as lateral flaps for closing the nappy round the wearer's waist.
Generally speaking, in the prior art machines, the lateral closure flaps are applied along certain stretches of a continuous web of a material for making nappies, these stretches corresponding to the single nappies, when subsequently divided.
These machines comprise a conveyor for feeding a continuous strip of elastomeric material, a unit for cutting a continuous strip of elastomeric material into suitably shaped single pieces constituting the lateral flaps for closing the nappies, and a unit for applying pairs of lateral flaps to the continuous band.
The cutting unit makes a succession of pieces forming the above-mentioned lateral flaps which are fed by a conveyor roller to the unit for applying the pairs of lateral flaps.
More in detail, each pair of lateral flaps is defined by a first and a second piece, and the cutting unit makes a continuous and alternating succession of first and second pieces.
Between the conveyor roller and the application unit, the machine has a pair of spacer rollers, which are able to pick up respective pieces from the continuous succession fed by the conveyor roller.
A first spacer roller picks up from the succession only the first pieces, whilst the second picks up only the second pieces.
The first and the second roller feed the respective pieces to the application unit, which makes the respective pairs of first and second pieces, which are mutually aligned and spaced by a predetermined length on the basis of the transversal dimensions of the continuous band of a material for making nappies. The application unit then applies in step each pair on the continuous band.
A solution of this kind, for example, is known from patent publication WO2014/087293 in the name of the same Applicant as this invention.
More specifically, the solution shown in that document describes a device in which the application unit is defined by a spacer roller configured to move the two pieces of material of the pair of accessory elements away from each other, so as to bring them to an operating distance for applying the band of absorbent material.
More specifically, the patent document WO2014/087293 specifies that the axial movement of the two pieces along the spacer roller is obtained by mechanical means, such as, for example, gears, gear wheels or cams, connected to the means for rotating the roller, or transfer rollers, so as to link the movements to each other.
However, it is known how, with the variation in the type of absorbent article to be made, the dimensions and the format of the lateral flaps also vary.
It follows that the distance between the two pieces of the single pair must vary as a function of the size of the article, thus resulting in a resetting of the entire kinematic mechanism for moving and transferring the accessory elements.
In effect, since they are connected to each other by mechanical transmission means, it follows that the rotation speed of the roller is linked to the distance of separation between the tabs, and the feed speed of the various components is also linked.
Consequently, the prior art machines, even though they have high levels of performance and production rates, have major drawbacks linked to the maintenance and setup times during size change-overs.